Mobile devices in communication with a mobile telecommunications network perform a plurality of measurements on the physical layer. For example, User Equipment (UE) for Long Term Evolution (LTE) is required to measure the radio characteristics as specified in document 3GPP TS 36.214 (V11.1.0). The measurements are reported to higher layers and are used for a variety of purposes including intra- and inter-frequency handover, inter-Radio Access Technology (inter-RAT) handover, timing measurements and Radio Research Management (RRM).
Reference Signal Received Power (RSRP) is one of the most basic physical layer measurements performed by the UE. The RSRP is defined in document 3GPP TS 36.214, Sect. 5.1.1, as the linear average in frequency space over the power contributions of those resource elements that carry Cell-specific Reference Signals (CRSs) within the considered measurement frequency bandwidth. The CRSs are specified in document 3GPP TS 36.211 (V11.5.0).
While LTE does not specify the number of resource elements underlying the RSRP measurement according to document 3GPP TS 36.214 (V11.1.0), the RSRP measurement has to meet accuracy requirements. For example, an accuracy requirement in the range of ±6 dB to ±11 dB has to be fulfilled, e.g., depending on noise level and environmental conditions. The difference in RSRP between two cells on different frequencies has to be measured with an accuracy of ±6 dB (which is also referred to inter-frequency measurement). Measuring the difference in RSRP between two cells on the same frequency is a more accurate measurement for which the requirements vary from ±2 dB to ±3 dB (which is also referred to as intra-frequency measurement).
In LTE according to the releases 10 and 11, Heterogeneous Networks (HetNet) are introduced for improving data throughput of the mobile telecommunications network. Due to overlapping areas covered by different cells, the RSRP measurement has to be performed in the presence of strong intra-frequency interference from other cells in case of CRS colliding. The CRS of an interfering cell can be up to 6 dB higher than the CRS of a target cell in release 10 and up to 9 dB higher than the target cell in release 11.
Conventionally, the RSRP is measured by computing a coarse channel estimation based on a de-rotation of the received CRS. The coarse channel estimation is filtered to reduce noise contributions. The RSRP results from the filtered channel estimation after compensating a gain factor of an Automatic Gain Control (AGC) or a gain factor of the downlink chain. However, the measurement accuracy of the conventional RSRP measurement can be degraded by intra-frequency interference so that a 3GPP requirement for the measurement accuracy cannot be fulfilled under all channel conditions or cellular network topologies, e.g., in LTE networks according to release 11.